in
Brufau J. (ed.), Tacon A. (ed.).
Feed manufacturing in the Mediterranean region: Recent advances in research and technology
Zaragoza : CIHEAM
Cahiers Options Méditerranéennes; n. 37 1999
pages 347-363
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Recent advances in research and technology. Zaragoza : CIHEAM, 1999. p. 347-363 (Cahiers Options Méditerranéennes; n. 37)
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Importance of vitamin E in the oxidative stability of meat:
Organoleptic qualities and consequences
E. Berges
Roche Vitaminas, S.A., Mar Mediterráneo 5, Pol. Ind. No. 1, 28850 San Fernando de Henares, Madrid, Spain
SUMMARY -The principal factors determining the organoleptic quality of meat are tenderness, colour, and flavour. Storage of meat often leads to the development of abnormal odours and tastes and loss of colour.
Oxidation of the lipids of meat and meat byproducts can be effectively controlled with antioxidants. This article explains how oxidation of lipids and deterioration in the organoleptic quality of meat occur and how these phenomena can be minimized by including a-tocopherol in animal diets. Dietary a-tocopherol is deposited in
muscle and fat during the life of the animal and protects against meat oxidation after slaughter.
words: Oxidation, lipids, muscle, a-tocopherol, vitamin quality, cholesterol.
RESUME
-
"Importance de la vitamine E dans la stabilité oxydative de la viande : qualités organolepfiques et conséquences: Les principaux facteurs qui déterminent la qualité organoleptique de la viande sont la tendreté, la couleur, et la flaveur. Le stockage de la viande mène souvent au développement d'odeurs et de goûts anormaux et à une perte de couleur. L'oxydation des lipides de la viande et produits dérivés de la viande peut être effectivement maîtris6e avec des anfioxydants. Cet article explique comment ont lieu l'oxydation des lipides et la détérioration de la qualité organoleptique de la viande et comment ces phénomènes peuvent être minimisés en incorporant de l'a-focophérol dans les régimes animaux. L'a-tocophérol alimentaire est déposé dans le muscle et le gras pendant la vie de l'animal et protège contre l'oxydation de la viande après I'abaítage.Mots-clés : Oxydation, lipides, muscle, a-tocophérol, vitamine E, qualité, cholestérol.
Meat can be defined as the product that results from the continuous changes that occur in muscle after the death of the animal (Sañudo, 1992). Meat is a highly nutritious food that contains high-quality protein, minerals, essential trace elements, and vitamins, in particular those of group B. In addition to its nutritive value, meat has other qualities, in particular its flavour, that increase its value and attractiveness.
Despite these positive attributes, consumption of meat has fallen in recent years. Consumers are demanding ever healthier and safer foods.
The principal factors determining the organoleptic quality of meat are tenderness, colour, and flavour, the latter being composed in turn of the two distinct factors taste and odor.
Though the concept of "quality of meat" is very ambiguous, high-quality meat may be defined as meat that satisfies the needs and demands of consumers, in particular those relating to organoleptic quality, nutritional quality, hygienic quality, and suitability for processing.
Prominent among new dietary trends is an increase in the consumption of frozen, processed, and precooked meat. This implies less consumption of fresh meat and favours oxidation and deterioration of meat. Recent human medical studies have confirmed the importance of certain polyunsaturated fatty acids in the prevention of pathologic processes (cardiovascular diseases, arthritis, inflammatory processes, etc.). There is also a trend towards modifying the fatty acid profile of meat in the sense of increasing the ratio of polyunsaturated to saturated fatty acids.
347
Oxidation of the lipids of meat and meat products depends on a number of factors. Prominent among these are the polyunsaturated fatty acid composition of the fat of muscle and other tissues, fatty acids (mostly unsaturated) present in the muscle membrane, the presence of prooxidants such as iron, the lipid composition of feed, and the presence of antioxidants.
Storage of meat often leads to the development of abnormal odors and tastes and loss of colour.
The major challenge facing the meat production and distribution industry is how to prevent rapid
oxidation and resulting loss of flavour and acceptability of fresh meat, processed meat, and precooked meat products.
The changes that occur after oxidation of meat are generally quantified by measurement of secondary degradation products. Data are expressed as TBARS (thiobarbituric acid reactive
substances). The TBARS value is generally regarded as a good indicator of the degree of deterioration of the organoleptic characteristics of meat as a result of oxidation.
Oxidation of the lipids of meat and meat subproducts can be effectively controlled with antioxidants. Many recent studies have dealt with the use of synthetic antioxidants. Nevertheless,
consumers are now becoming increasingly health-conscious and resistant to the use of synthetic antioxidants.
There is now considerable interest in the actions of a variety of natural antioxidants such as extracts of vegetables, fruits, grains, spices, and herbs. Vitamin E has been shown to be an effective antioxidant, especially when included in animal diets, and is accepted by consumers on the basis that it is a naturally occurring substance.
Oxidation lipids Oxidation of
Lipid oxidation is an autocatalytic process that occurs in foods and biological membranes.
Most of the oxygen utilized by cells is reduced in the mitochondria, while a small amount is used in reactions that take place in the cytosol, the nucleus, and the cell membrane. This latter oxygen
generally receives four electrons after generating a number of molecules of NADH that ultimately increase energy content via ATP. Via the action of certain oxidises, however, it can receive only one electron, giving rise to the production of a superoxide anion (0;') or hydrogen peroxide (H202). The O;' anion is one of the principal free radicals that initiate cellular oxidation processes (Fig. 1). It can react with H202 to form the even more aggressive hydroxyl radical (*OH).
I
PUFA RH1
* +
+ OxygenFatty acid radical R
---m Peroxide radical ROO
Fe2'/Cu'
+
+ PUFA RHHydroperoxide f Fatty acid radical
ROOH R
t
Aldehydes, ketones, acids, epoxides, polymers, etc.
Fig. 1. Oxidation of lipids.
Free radicals can also be formed via the metabolism of neutrophils and macrophages and by the action of the lytic enzymes of these. They can also be exogenous molecules.
The presence of transition metals such as Fe2+ and Cu' favours the formation of highly reactive free radicals.
These oxidation phenomena are favoured by the following factors, among others:
(i) Level of unsaturated fatty acids in meat.
(i¡) Free radicals, myoglobin, hemoglobin, cytochromes, metals such as iron and copper and other heavy metals.
(iii) Conditions of slaughter (stress, pH, temperature of the carcass, electrical stimulation).
(¡v) Rupture of the integrity of muscle membranes (mechanical deboning, grinding, processing, and cooking).
Effect on the of meat
As a result of the peroxidation that occurs in living animals and the oxidative rancidity that starts to develop shortly after slaughter, polyunsaturated fatty acids are broken down into short-chain
compounds (aldehydes, ketones, acids, epoxides, polymers, etc.). These give rise to unpleasant odors and tastes that reduce the acceptability of the meat to the consumer.
Discoloration of meat is due to oxidative processes and to reductant enzymatic systems involved in the control of metmyoglobin levels (Faustman and Cassens, 1990).
As a result of the oxidative processes oxymyoglobin is generated and the meat acquires a bright red colour and subsequently a brown-red colour as a result of formation of metmyoglobin. This gives the meat an undesirable appearance that is rejected by consumers (Fig. 2).
Globin
>Fet2<
o2
Globin
>Fet3<
HOH
Deoxy-M b Oxy-M b Met-Mb
Purple red Bright red Brown red
Fig. 2. Colour of meat and associated forms of myoglobin (Faustman and Cassens, 1989).
Renerre ef al. (1996) observed that during the maturation of meat the content of metmyoglobin (met-Mb) and lipofuscin is greater in muscles with greater instability of colour.
These oxidative processes are even more pronounced in precooked meat. Precooking results in abnormal odors and tastes ("warmed-over flavour"). The same processes occur also in meat that is ground and exposed to the air.
Other studies have demonstrated that as well as causing colour changes, loss of cellular integrity causes the meat to exude a greater amount of water (Monahan ef a/.
,
1990).349
Vitamin E General
At least eight compounds with vitamin E activity have been isolated from the oils of plants. These compounds are a, ß, y, and 6-tocopherol and a, ß, y, and 6-tocotrienol. They are all chemically different. The principal characteristic of the trienols is their unsaturated condition at carbon atoms 3, 7, and 11 of the chain, whereas in tocopherols the corresponding carbon atoms are saturated. The nomenclature a, ß, y, and 6 used for tocopherols and tocotrienols indicates the number and position of the methyl groups. This is shown in Fig. 3, in which the hydrophilic and hydrophobic parts of the molecules can also be seen.
R3
Hydrophilic R' Hydrophobic
HO
'
R'
Compound R' R' R3
a-tocopherol CH3 CH3 CH3
ß-tocopherol CH3 H CH3
y-tocopherol H CH3 CH3
6-tocopherol . H CH3
Fig. 3. Chemical structure of tocopherols.
"Vitamin E is a generic term used for all tocopherols and tocotrienols, as all exert the same biological action. The efficacy with which they do so is very low in the case of the tocotrienols, whereas tocopherols, and in particular a-tocopherol, are much more active and potent and account for almost all the vitamin E activity of living tissues.
Absorption of vitamin E occurs mostly via the lymphatic system, the molecules being transported to the liver inside triglyceride-rich chylomicrons. Vitamin E is then secreted by the liver and incorporated into very-low-density lipoproteins (VLDL). It is transported to the interior of cells inside low-density lipoproteins (LDL), which are recognized and removed from the plasma by LDL-specific receptors.
Vitamin E deficiency can lead to lesions of the reproductive, nervous, cardiovascular, and
musculoskeletal systems and the liver. Vitamin E acts as an immunomodulator, however its most important function is as an in vivo antioxidant that protects fatty tissues from attack by free radicals.
Vitamin E is found in biological membranes in a system stabilized by physicochemical forces that include lipid-lipid interactions between a-tocopherol and polyunsaturated phospholipids. At this site (Fig. 4) a-tocopherol protects polyunsaturated fatty acids, which are extremely susceptible to oxidation, from peroxidation by free radicals produced in many cases by enzymes of the membrane itself (NADPH oxidase).
Though vitamin plays a crucial role as an antioxidant in cell membranes, its concentration can be as low as one molecule per 2,000 to 3,000 lipid molecules.
Despite this low molar concentration in the membrane, vitamin E is the principal lipid-soluble antioxidant that acts at the level of cellular membranes to prevent peroxidation and to modulate the metabolism of arachidonic acid initiated by lipooxygenase and/or cyclooxygenase.
'
HO
Exterior
Fig. 4. Localization of vitamin E in the cell membrane.
of vitamin E in tissues
Differences in the affinity of a-tocopherol for cellular membranes and for various organs and
tissues result in different concentrations of the substance at different sites. Two important factors that determine the concentration of the substance are the duration and amount of dietary supplementation.
In a study in which the diet of broilers was supplemented with 200 mg of a-tocopherol acetate per kg of feed for variable periods (l, 2, 3, 4, and 5 weeks prior to slaughter), Brandon et al. (1993) found a-tocopherol concentration to vary considerably between tissues, being highest in the heart, lowest in the brain, and intermediate in the lungs, liver, thigh, and breast. In the case of the heart the highest concentration was reached with three weeks of supplementation prior to slaughter, whereas
in
the case of thigh and breast a period of four weeks was required (Fig. 5).25
T
20
15
10
5
U
I
Thigh Breast
o t
l I I i 1 tO 1 2 4 5
Weeks before slaughter with suppl. of 200 mg/kg
Fig. 5. Deposition of vitamin E in various muscles of the broiler.
351
There are important differences between chickens and turkeys in terms of the efficacy of deposition of vitamin E, the latter animals being less efficient in terms of deposition of a-tocopherol both in fat and in muscle (Mecchi et al., 1956; Marusich et al., 1994) (Table 1). The fact that levels of vitamin E are lower in turkeys appears to be due to greater production and excretion of products derived from the catalytic metabolism of tocopherol (tocopheryl glucuronides), the extent of this being two to nine times greater in turkeys than in chickens (Jones, 1989).
Table 1. Deposition of vitamin in the breast of chickens and turkeys (Marusich et al., 1994) Suppl. vit. E IU vit. E ingested/day/kg live wt a-tocopherol (mg/kg) in breast
(IU/kg feed) (43-56 days) (Age: 8 weeks)
Chicken 40 2.57 5.0
Turkey 37 2.92 1.4
Sheldon et a/. (1984) found that the muscle of the thigh of turkeys can contain up to six times as much a-tocopherol as the breast or fat, presumably because of the greater vascularity of the leg of the turkey.
The lower concentration of a-tocopherol in turkey meat that results from less efficient deposition renders turkey meat susceptible to oxidation and explains the greater vitamin E requirements of this species as compared with chickens.
Studies on beef cattle have confirmed that deposition of vitamin E in cellular membranes increases the a-tocopherol content of muscle. This can be seen in Fig. 6 (control or 1,200 mg vitamin
E
per calf per day) and Fig. 7 (200, 850, or 2,000 mg vitamin E per calf per day).This has major consequences in terms of the organoleptic characteristics of meat.
r-
6.4Holstein breeds Meat suitability
I
Control Cl 1200 mg vit. E/calf/day1
Fig. 6. Increase in vitamin E content of muscle due to dietary supplementation (Mitsumoto et al., 1991).
If the vitamin E content of meat is less than that recommended, all the oxidative processes that give rise to metmyoglobin commence very rapidly, giving rise to an undesirable colour.
Fig. 7. Increase in vitamin E content of muscle by dietary supplementation (20,000, 85,000, or 200,000 mg of vitamin E in the last 100 days of feeding before slaughter) (Institut de
1996, unpublished data).
The quality of meat can be impaired in three principal ways: (i) microbiologic contamination;
(i) discoloration; and (iii) lipid oxidation.
Vitamin E plays a very important role in preventing the latter two of these.
Vitamin E and prevention lipid oxidation
The presence or absence of vitamin E in animal tissues has a critical influence on the stability
of
lipids during the storage of meat. By trapping free radicals (Figs 8 and g), Vitamin protects fatty acids and cholesterol from oxidation. In this process vitamin E releases a hydrogen atom, which is captured by a peroxyl radical which is thereby reduced to form a hydroperoxide. Vitamin E radicals are extremely stable and do not react with polyunsaturated fatty acids. They can also react with other radicals and thus terminate the chain of reactions
of
lipid oxidation at this point.CH3
Highly stable intermediate compound
Fig. 8. Antioxidant effect of vitamin E.
y
CH, TerminaJion.O
Vit.
C (red.)*n
.,
vit. c
+a-toc.
CH3 RegenerationFig. 9. Antioxidant effect of vitamin E.
Vitamin E is highly efficient as an antioxidant. From chemical and biochemical studies it is known that after being oxidized and before undergoing decomposition, vitamin E can be re-reduced. Ascorbic acid (vitamin C) and the enzyme glutathione are the principal water-soluble intracellular antioxidants (reductants) that generate reduced vitamin E (Fig. 9). This reaction depends on the concentration of these substances andlor of the enzymes that maintain them in their reduced form.
Effect of composition and quality of dietary fat on lipid Oxidation of meat. Antioxidant effect of vitamin E
Both the composition and the quality of dietary fat influence the oxidative stability of meat during storage.
The more unsaturated is the dietary fat, the more unsaturated will be the fat of muscles and membranes. A number of studies have shown that meat with a high content of polyunsaturated fatty acids is more susceptible to oxidation and that the antioxidant effect of vitamin E plays an important role in the prevention of this oxidation.
Lin et a/. (1989a) found that dietary supplementation with coconut oil, olive oil, linseed oil, and partially hydrogenated soybean oil modified the lipid profile of meat derived from broiler chickens.
They also found that meat produced with a diet rich in linseed oil, which has a high content of a-linolenic acid (0-3), was more susceptible to oxidation. Addition of 100 mg of a-tocopherol acetate per kg of feed significantly improved the oxidative stability of the chicken meat.
In a recent study by Ajuyah et a/. (1993) it was found that addition of linseed oil to chicken feed increased the content of a-linolenic acid (0-3) in the meat produced. In view of the need to protect this meat from oxidative processes, the authors compared the efficacy of canthaxanthin and a-tocopherol as antioxidants. It was found that a-tocopherol had a greater antioxidant effect.
Miller et a/. (1993) studied the effect of dietary supplementation with O, I O , or 20 g of fish oil and 50, 250, or 450 mg of a-tocopherol acetate per kg of feed for 52 days. Supplementation with fish oil reduced the 0-6/0-3 ratio from 10.2 to 1.3 in breast and from 16.1 to 2.1 in thigh. Supplementation with a-tocopherol acetate significantly increased the resistance of the meat to oxidation.
inclusion of oxidized oils in animals' diets leads to a reduction in the concentration of a-tocopherol in muscle tissue. From the results referred to above it can be concluded that the use of low-quality (oxidized) fats and oils in animals' diets calls for an increase in dietary a-tocopherol in order to counteract the oxidative stress suffered by tissues, meat, and meat derivatives (Sheehy et al., 1993b,c).
Effect of vitamin on oxidation of cholesterol
Cholesterol, which is present in cellular membranes, is susceptible to oxidative processes initiated by free radicals. Concern about the presence of cholesterol oxidation products (COPs) has increased in recent years. Scientific opinion has linked the presence of these compounds (7-ketocholesterol, 25- hydroxycholesterol, cholestane triol, etc.) to the development of atherosclerotic lesions (Steinberg et al., 1989).
López Bote et al. (1 992) studied the effect of supplementation with vitamin E and spice extracts in terms of prevention of lipid and cholesterol oxidation in chicken meat. The TBARS values with the four treatments (control, rosemary, sage, and 200 IU of vitamin E per kg) were 0.51, 0.30, and 0.25, respectively. The concentration of COPs in cooked meat was 44, 42, and lower in the rosemary, sage, and vitamin E groups, respectively, than in the control group.
Galvin ef a/. (unpublished data) found production of COPs to be inversely related to the concentration of a-tocopherol acetate in the diet. The concentration of COPs in the muscle of chickens given 200 and 400 mg of a-tocopherol acetate per kg of feed was respectively 75 and 51 % of that found in the muscle of chickens given 100 mg of a-tocopherol acetate (Fig. IO).
COPS
400 Vitamin (mglkg)
Fig. 10. COPs in muscle of chicken. Cooked and stored for 5
Galvin et a/. (1995) determined the effect of storage of meat and supplementation with a-tocopherol acetate on the formation of COPs (25-hydroxycholesterol,
7-ketocholesterol, etc.) in the breast and thigh of chickens. The diet was supplemented with 20, 200, or 800 mg of a-tocopherol acetate per kg of feed. The samples of meat were cooked,
All the samples were found to contain 25-hydroxycholesteroI immediately after cooking; 20-a-hydroxycholesterol was detected in breast meat from day 6; and 7-ketocholesterol was detected in breast and thigh meat from day 12. The total amount of COPs did not increase appreciably until day 12 of storage. Supplementation with 200 and 800 mg of a-tocopherol acetate per kg of feed reduced the level of COPs by 4 0 4 0 % and 60-70%, respectively, in both breast and thigh.
Effect of vitamin E on the organoleptic qualities of meat
Deposition
of
vitamin E in cellular membranes increases the a-tocopherol content of muscle, and this has very important consequences in terms of the organoleptic qualities of the meat.Supplementation of the diet with vitamin E increases the concentration of a-tocopherol in membranes, especially those of mitochondria and microsomes, and thus significantly reduces the susceptibility of membranes to lipid oxidation (Monahan et al., 1990; Ashgar et al., 1991; Mitsumoto et al., 1991).
The degree of oxidation of meat is generally assessed by measuring the content of secondary degradation products that arise from oxidation of polyunsaturated fatty acids. The analytical method uses substances that react with thiobarbituric acid (TBARS value) as a measure of the degree of this oxidation. A higher TBARS value indicates a greater degree of oxidation of meat. The time-course of TBARS values in meat and the effect of vitamin E in preventing oxidation are seen in Table 2.
Table 2. Time-course of TBARS value of meat in relation to vitamin E content (Faustman et al., 1989)'
a-tocopherol TBARS
(glkg of meat)
O months 1.5 months 3 months
Control 1.6 0.1 1 1 .lga 1 .48a
Vitamin E 4.4 0.13 0.1 3b 0.26b
'Pieces of loin frozen at
a,b: Values marked with different letters are significantly different P<0.05
The TBARS value also depends on the content of polyunsaturated fatty acids (PUFAs) in the diet.
Walsh et a/. (1992) found that the degree of oxidation of the meat of calves fed on a vitamin E-deficient diet varied significantly with the PUFA content of the diet, being greater in animals fed on a diet with a higher PUFA content.
Colour is the principal factor determining the acceptability of meat to the consumer (Faustman and Cassens, 1989).
In a study performed at the Institut de l'élevage (France, 1996) it was found that global appreciation of steak with a low content of vitamin E that had been on display for '13 days was much lower than that of steak with adequate levels of vitamin E that had been on display for the same period, significant differences being present from as early as day 7 (Fig. 11).
D+5
* ***
D+9
Vit. E 100 Vit. E 200
Period on display
Global appreciation of meat as a function of time on display (Institut de l'élevage, France, 1996, unpublished data).
356
The same study included an analysis of the shelf life -as measured by change in colour and organoleptic characteristics- of various cuts of meat kept under plastic film or in a modified atmosphere. As seen from Fig 12, the shelf life of the meat was greater where higher levels of
supplementation with vitamin E had been given.
A. plastic film B. In modified
All muscles Sirloin Tenderloin All muscles Sirloin Tenderloin
Fig. 12. A: Shelf life of meat under plastic film; or B: in a modified atmosphere as a function of level of supplementation of diet with vitamin (Institut de l'élevage, France, 1996, unpublished data).
Supplementation of calves' diets with vitamin leads to an increase of 1.5 to 6 days in the time meat can be displayed in the butcher's shop without suffering changes in its organoleptic qualities.
This conclusion was reached in the recent review by Willians and is shown in Table 3.
Table 3. Increase in shelf life of meat (in days) as a function of supplementation of calves and concentration of vitamin E in the meat (Willians, 1992)
Study Dose vitamin Concentration Increase in shelf life
(mg/day) a-tocopherol of meat due to
(mglkg loin) suppl. (days)'
Basal O
1 300
2 1140
3 360
1280 4 2080
3520
5 1200
1.4 3.8 6.2 4.1 6.8 6.7 7.6 3.5
O 5.3 2.0 2.5 4.0 3.1 5.2 4.8
'Meat from calves supplemented with vitamin E as compared with meat from unsupplemented calves
In this context it is necessary to consider the amount of supplement given daily and the period over which it is given. The concentration of vitamin in plasma and muscle depends on the amount of supplement given and is lower with less supplementation (Walsh et al., 1992).
Khattak et al. (1995) studied oxidation of the meat of chickens fed with either rapeseed oil or fish oil. The degree oxidation (TBARS value) was found to be greater in meat produced with fish oil,
16 days) or frozen (-20°C for 90 days).
Supplementation of the diet with 300 mg of a-tocopherol acetate reduced the value in both fresh and frozen meat with both types of diet.
357
Wen et a/. (1 996) measured the effect of supplementation of a commercial turkey diet with 20, 300, or 600 mg of a-tocopherol acetate per kg firstly on the TBARS value of raw and cooked turkey meat
(-2O"C), and secondly on the a-tocopherol content of the meat. They found that supplementation with a-tocopherol acetate significantly reduced (Pc0.01) the TBARS value of meat regardless of whether the meat was raw or cooked or had been refrigerated or frozen.
The a-tocopherol content of the refrigerated meat showed no variation, whereas after four months of storage that of the frozen raw hamburgers had fallen from 5.67 to 3.54 and from 3.56 to 2.3 mg/kg in the 600 and 300 ppm treatment groups, respectively. After five months of treatment the a- tocopherol content of the frozen cooked hamburgers had fallen from 5.6 to 2.88 and from 3.29 to l .85 mglkg in the 600 and 300 ppm treatment groups, respectively.
The authors suggest that the fact that the a-tocopherol content of the refrigerated meat was
maintained could be because at the temperatures concerned oxidation reactions occur in a liquid/liquid phase in which, together with a-tocopherol, water-soluble antioxidants help to prevent oxidation. The great capacity of vitamin E to act as an effective antioxidant at the concentrations at which it is present in the membrane is due also to its ability to be re-reduced from the radical to the active form by other intracellular reductants (Morrisey, 1994b).
In frozen meat, some catalysts and antioxidants remain trapped in the solid (frozen) phase and the antioxidant activity of the cytosolic phase does not function optimally. In addition, free lipid radicals are soluble in the lipid fraction and more stable at low temperatures. This allows them to diffuse over considerable distances and thus extend the oxidation reaction. Being lipid-soluble, vitamin E acts as the first line of antioxidant defense and can thus be consumed rapidly.
A problem of great economic importance in the marketing of meat is formation of PS€ meat (pale, soft, and exudative). By increasing metabolic rate, stress prior to slaughter causes accumulation of lactic acid and thus a fall in the pH of muscle. Tenderness of meat diminishes as final pH diminishes, and colour is also affected.
The occurrence of PSE meat in chickens and turkeys is due to an over-reaction of the animals to stress. Animals deficient in vitamin E have high plasma levels of pyruvate kinase and creatine kinase as a result of damage to cellular membranes by free radicals. Increased deposition of a-tocopherol in cellular and subcellular membranes of muscle as a result of increased dietary supplementation not only improves the integrity of membranes, but also influences the degree to which PSE meat is
formed.
Ferket et a/. (1994) found that the incidence of PSE meat fell when the diet of turkeys was supplemented with 200 IU of vitamin E for two to three weeks prior to slaughter. Also, the longer the period of supplementation, the lower was the incidence of PSE meat. This effect appears to be related to the amount of vitamin E incorporated into muscular tissue: the greater the amount
of
vitamin E present, the greater is the capacity of the muscle to counteract oxygen-reactive metabolites produced during the stress reaction.In an unpublished study on pigs, Monahan et a/. found that in this species also, supplementation with 200 mg of a-tocopherol per kg of feed for 14 weeks led to a reduction in exudative losses from fresh chops (Fig. 13).
Supplementation with 200 IU of vitamin E also maintained the original colour (Hunter "a" value) of both fresh and frozen chops (Fig. 14).
Piretti et a/. (1995) studied the effect of supplementation with vitamin E on the TBARS value of the fat and muscle of ham during maturation (Fig. 15). Supplementation with 250 mg of a-tocopherol per kg of feed led to a fall in the degree of oxidation.
Schaefer et al. traced control samples of beef and samples of beef with an adequate level of vitamin E sent to three different distribution centres in Las Vegas, Lenexa, and Houston. They found the percentage losses due to discoloration (Table 4).
Fig. 13.
Fig. 14.
Fig. 15.
0
.-
2 4 6 8
of
14 weeks
Effect of dietary vitamin on exudative losses (%) from fresh pork chops (Monahan al., unpublished data).
Dietary vitamin Vit. E 1 O
L - . ! - Vit. E 1 O0
_-
i_' Vit. E Z O O
Freezing = 4 months
chops chops
of
Effect of vitamin E on the fall in the Hunter "al' value of fresh and frozen pork chops (Monahan et al., 1993).
4.5 7 4.2 1
4 8 1 2 '
_ _ -- - -___ ---
G Vit. E 250 '
Mean TBARS values in the fat of ham during maturation ("Pc0.05)
359
Table 4. Fall in price of meat due to discoloration (% of initial value) Control Vitamin E
Las Vegas 9.09 3.27 Lenexa 4.27 2.45
Houston 4.68 0.32
Mean 5.62 1.98
The improvement obtained by adding vitamin E was significant, there being a 65% reduction in losses due to discoloration, a figure consistent with other results cited above.
Figure 16, which shows results obtained in a recent study by Brad Morgan, of the University of Oklahoma, shows the approximate cost of vitamin E supplementation and the benefit that such
supplementation brings to the meat producer and trader. The producer is able to supply meat of higher quality that should fetch a higher price, while the trader benefits from the smaller losses due to exudation and discoloration of the meat and is able to market a product of higher organoleptic and nutritional quality.
C o s t Producer's Trader's
benefit benefit
Fig. 16. Benefit of vitamin E supplementation in terms of smaller losses due to discoloration of meat (Brad Morgan, 1997, Oklahoma State University, Department of Animal Science).
References
Afaf Kamal-Eldin and Lars-Ake Appelqvist. (1996). The chemistry and antioxidant properties of tocopherols and tocotrienols. Lipids, 31, No. 7.
Ajuyah, A.O. (1993). Effect of dietary full-fat flax seed with and without antioxidant on the fatty acid composition of major lipid classes of chicken meats. Sci., 72, No. 1.
Ajuayah, A.O. et al, (1993). Dietary antioxidants and storage affect chemical characteristics of fatty acid enriched broiler chicken meats. J. Food Sci., 58, No. 1.
Ang, C.Y.W. (1988). Comparison of broiler tissues for oxidative changes after cooking and refrigerated storage. J. Food Sci., 53, No. 4.
Ang, C.Y.W. and Lyon, (1990). Evaluations of warmed-over flavour during chill storage of cooked broiler breast, thigh and skin by chemical, instrumental and sensory methods. J. Food Sci., 55, No. 3.
Asghar, A. et al, (1989). Influence of oxidised dietary oil and antioxidant supplementation on membrane-bound lipid stability in broiler meat. Brit. Poultry Sci.
Asghar, A. et al. (1991). J. Sci. Food Agr.
Asghar, A., Gray, J.I., Buckley, D.J., Lin, C.F., Booren, A.M. and Flegal. (1989). Effects of dietary oils and a-tocopherol supplementation on lipid composition and stability of broiler meat. J. Food Sci., 54, No. 6.
Asghar, A., Gray, J.I., Buckley, Pearson, A.M. and Booren, A.M. (1988). Perspectives on warmed-over flavour. Food Technol., 42, No. 6.
Bartov, I. and Frigg, M. (1992). Effect of high concentrations of dietary vitamin E during various age periods on performance, plasma vitamin E and meat stability of broiler chicks at 7 weeks of age.
Brit. Poultry Sci.
Blum, J.C. et al. Influence des apports élevés de vitamine E sur les performances de croissance du
"broiler" et la conservation des carcasses réfrigérées. Alimentation Nutrition.
Blum, J.C., Touraille, C., Salichon, M.R., Ricard, F.H. and Frigg, M. (1990). Effect of dietary vitamin E supplies in broilers. 2"d Report: Male and female growth rate, viability, immune response, fat content and meat flavour variations during storage.
Buckley, D.J., Gray, J.I., et al. (1989). Effects of dietary antioxidants and oxidised oil on membrana1 lipid stability and pork products quality. J. Food Sci., 54: 11 93-1 197.
Buckley, D.J. and Morrissey, P.A. Vitamin E and meat quality. Roche publication.
Clermont-Ferrand (1992). 38th lnternational Congress of Meat Science and Technology, 1992.
Crystal, R.G. and Ramón, J.R. (1992). GSH System. Glutatión: €je de la defensa antioxidante.
Etsuo Niki. (1 987). Inhibition of oxidation of liposomal and biomembranes by vitamin E. Clinical and nutritional aspects of vitamin E. Elsevier Science Publishers, 1987.
Faustman, C. (1 993). Food from supplement-fed animals. Technology reduced-additive foods.
Faustman, C., Cassens, R.G. et al. (1 989a). J. Food Sci., 54: 485.
Faustman, C., Cassens, R.G. et al. (1989b). J. Food Sci., 54: 85%.
Faustman, C., Cassens, R.G. (1990). J. Muscle Foods, 1: 217.
Ferket, P. and Allen, (1994). How nutrition and management influence PSE in poultry meat. Broiler Industry, 57, No. 9.
Frigg, Research experiences with vitamin E for poultry meat quality. Vitamins and Fine Chemicals.
Research and Technology Development, Exploratory Research. F, Hoffmann- La Roche AG.
Goodwin, T.L. Current trends in poultry meat consumption and quality.
Gray. J.I. et al. (1996). Oxidative quality and shelf life of meats. Meat Sci., Vol. 43. Elsevier Science Ltd.
Gray, J.I., Pearson, A.M. (1994). Lipid-derived off-flavours in meat formation and inhibition. Flavour of Meat and Meat Products.
Jensen, C., Skibsted, L.H., Jakobsen, K, and Bertelsen. (1995). Dietary vitamin and quality of precooked chicken meat. Meat Focus International.
361
Kanner, J. and Bartov, I. Effect of high levels of dietary iron, iron injection, and dietary vitamin on the oxidative stability turkey meat during storage. Departments of Poultry Science and Food Science, Agricultural Research Organization.
Lester Packer and Sharon Landvik. (1989). Vitamin E: Biochemistry and health benefits. Vitamin E biochemistry and health implications.
Lin, C.F. et al. (1989). Effects of oxidised dietary oil and antioxidant supplementation on broiler growth and meat stability. Brit. Poultry Sci.
Marusich, W.L., De Ritter, E., Ogrinz, E.F., Keating, J., Mitrovic, M. and Bunnell, R.H. Effect supplemental vitamin in control of rancidity in poultry meat. Animal Health Research Department and Product Development Department, Hoffmann-La Roche Inc., Nutley, New Jersey.
Mecchi, E.P. et al. (1956). Further studies on tocopherol content and stability of carcass fat of chickens and turkeys. Poultry Sci., 35, No. 6.
Mecchi, E.P. et al. (1956). The role of tocopherol content in the comparative stability of chicken and turkey fat. Poultry Sci., 35, No. 6.
Mitsumoto, M. ef al. (1991). Improvement of colour and lipid stability in beef longissimus with dietary vitamin C dip treatment. J. Food Sci.
Monahan, F.J. et al. (1990). Meat Sci.
Ordoñez, J.A. Ampliación de la vida útil de la carne refrigerada mediante envasado a vacío y en atmósferas modificadas. Universidad Complutense de Madrid.
Piretti, M.V. et a/. (1995). Department of Biochemistry, University of Bologna. Meat International.
Poste, L.M. (1990). A sensory perspective of effect of feeds on flavour in meats: poultry meats. Food Research Centre, Research Branch, Agriculture Canada, Ottawa, Canada. J. Anim. Sci., 68, No. 12.
Proceedings 3dh International Congress of Meat Science and Technology (1 988).
Proceedings l lth European Symposium Quality of Poultry Meat, France (1 993).
Proceedings European Symposium on Poultry Nutrition (1 995).
Renerre, M. et al. (1996). Antioxidant enzyme activities in beef in relation to oxidation of lipid and myoglobin. INRA, Meat Sci., Vol. 43, Elsevier Science Ltd.
Resurreccion, V.A. and Reynolds, A.E. Jr. (1990). Evaluation of natural antioxidants in frankfurters containing chicken and pork. J. Food Sci., 55, No. 3.
Roncales, P. Evolución post-modem del músculo y calidad de la carne y los productos cárnicos.
University of Zaragoza, Spain.
Ruiz, J.A. et al. ß-carotene or a-tocopherol in feed improve the oxidative stability of poultry meat.
Sante, V. and Lacourt, A. (1994). The effect of dietary a-tocopherol supplementation and antioxidant spraying on colour stability and lipid oxidation of turkey meat. J. Sci, Food Agr.
Schaefer, D.M. et al. (1995). Enhancing colour and shelf life of meat products by antemorten incorporation of vitamins E and C and possibly ß-carotene into animal tissues. Animal Science Research and Development.
Sheehy, P.J.A. et al. Vitamin E as an antioxidant for turkey meat.
Sheehy, P.J.A., Morrissey, P.A. and Buckley, D.J. Advances in research and application vitamin as an antioxidant poultry meat. Departments of Nutrition and Food Technology, University College, Cork, Ireland.
Sheldon, B.W. (1984). Effect of dietary tocopherol on the oxidative stability of turkey meat. Poultry Sci., 63.
Snetsinger, D.C. (1975). Application of limited feeding programs for egg strain layers. Poultry Sci., 54, No. 5.
Wen, J. et al. (1996). Oxidative stability and a-tocopherol retention in turkey burgers during refrigerated and frozen storage as influenced by dietary a-tocopheryl acetate. Brit. Poultry Sci., 37.
Winne, A. and Dirinck, (1996). Studies on vitamin E and meat quality. Effect of feeding high vitamin E levels on chicken meat quality. J. Agr. Food Chem.
363
